Beta-Adrenergic receptors (Beta-ARs) modulate a variety of physiological responses, including the regulation of heart rate, smooth muscle contraction, gluconeogenesis and lipolysis. Three Beta-ARs (Betal-AR, Beta2-AR, and Beta3-AR) have been cloned, but data suggest that these three subtypes to do not account for all of the known physiological responses. Recent cloning of a novel avian Beta-AR in our lab (submitted for publication) further supports the evidence suggesting the existance of other Beta-ARs. In this project the novel avian Beta-AR gene (Beta4c- AR) will be used as a probe to screen a human genomic library at low stringency hybridization conditions in order to clone the human homologue of Beta4c-AR. Preliminary data from Southern hybridization analysis demonstrate that the Beta4c-AR probe hybridizes to human genonic DNA fragments that are different from those hybridized with a Beta2-AR and Beta3-AR probes. Clones obtained from the library will be analyzed by restriction enzyme fragment analysis and screened with Betal-AR, Beta2-AR, and Beta3-AR probes. Candidates of atypical Beta-ARs will be subcloned and sequenced. Sequences consistent with Beta-ARs will be expressed in COS cells and assessed for [125-Iliodocyanopindolol binding (a Beta-AR-specific antagonist). Ultimately pharmacological characterization and signal transduction mechanisms will be determined in the human homologue of Beta4c-AR .